This invention relates to a modem power supply, and more particularly to a telephone line modem which is directly coupled to a telephone network and which is at least partially powered by power which is supplied by the telephone network.
A telephone line modem is used to provide signal connections between an analog telephone line and for example a digital computer system. Electrical energy is required to power the modem. In the past, power has been provided by a local power source, such as a battery or a power supply coupled to the a.c. power mains. Since the power mains has been considered an adequate and reliable source of power, and since the power available on the telephone lines has been considered intermittent or insufficient and thus unreliable, it has been preferred to use reliable local power in connection with the functions of a modem.
Virtually all telephone sets have employed power from the telephone line to power the electronic circuitry as a matter of necessity and where local power is not indicated or available.
Local power is considered preferred. Attempts have been made to power modems from terminal or serial line power. Sources include Novation, for its Parrot modem, Black Box for its Tote-a-Modem, Migent and Teamworks. All of these approaches suffer one significant deficiency: power must be supplied to the analog portion of the modem from a local power source. Hence precious power is wasted. Battery powered-terminals in particular tend to run out of power quickly.
Circuitry is known for optical isolation, and charge pump circuitry is known for power inverter applications. Use in a telephone line modem in connection with a power supply has not been known.
There is a need to provide a low-power drain modem which requires no external power supplies.